This invention relates in general to oscillators and particularly to a high frequency oscillator that exhibits extremely low phase noise, will operate with low power supply potential and lends itself to integrated circuit implementation. In the preferred embodiment of the invention, a low phase noise, integrated circuit oscillator that free runs above 200 MHz with approximately 1.2 volts applied potential, results. In addition to the power supply connection pins (B+ and ground) for the integrated circuit, only a single "live" or signal connection pin is required. The minimization of the number of live pins, i.e. pins at which there are voltage changes, results in a highly stable oscillator exhibiting a low phase noise characteristic. Further, the oscillator of the invention operates with extremely low DC power voltages, which is compatible with the trend in integrated circuits toward low voltage, high frequency operation. Basically the oscillator requires a two diode voltage drop for operation, that is approximately 1.2 volts.
The inventive oscillator uses a current mirror that consists of three NPN transistors, with a fourth transistor being added for voltage balancing purposes. As is known, the three transistor current mirror is much less dependent upon Beta than the conventional two transistor mirror. It has been found that, by appropriate interconnection of a feedback path to a current node on the three transistor current mirror, a negative resistance region is formed. The steepness of the negative resistance region may be controlled by the amount of resistance in the feedback path which forms the basis for the oscillator. A conventional varactor diode tuning control is connectable to the single pin (as is the tuned circuit) for establishing the oscillator's fundamental frequency. The invention provides a very stable, high frequency, low operating voltage, readily integratable oscillator that exhibits very low phase noise.